Incremental timer drive mechanism

ABSTRACT

An incremental drive mechanism for a switch operating timing cam is disclosed. The mechanism includes a camshaft having a radially extending cam and a cooperating slide which is adapted to reciprocate along a rectilinear path. The slide has first and second cam surfaces which are engaged during a major portion of a single revolution of the camshaft to reciprocate the slide in a positive manner. The slide has a cantilever spring arm which carries a pawl tooth at its end to engage successive teeth provided on the periphery of a switch operating cam drum or disc. A cantilever leaf spring is provided which bears against the slide to urge the pawl tooth into engagement with the cam disc or drum in the event the cantilever spring arm becomes permanently displaced toward the slide.

This application is a continuation-in-part of application Ser. No.07/056,002, filed June 1, 1987, now U.S. Pat. No. 4,760,219.

BACKGROUND OF THE INVENTION

This invention relates to timing mechanisms, and more particularly todrive mechanisms for incrementally advancing the timing cam of anappliance timer.

Although the principles of the present invention may be included invarious timers, a particular application is made in timers of the typeemployed to control the various circuits and functions of automaticlaundry appliances, such as washers and dryers. Appliance timersbasically comprise a rotatable member having a plurality of projectingcams which sequentially engage switch members, which, in turn, controlthe various operations of the appliance.

Basically, there are two types of timers for home appliances. One suchtimer is a cylindrical, rotary drum having a plurality of camsprojecting from its surface which engage switch members, and is quitesimilar to a music box. An example of such an arrangement is shown inU.S. Pat. No. 3,395,585. Another such timer is described in U.S. Pat.No. 2,703,347. In the latter-mentioned patent, the timing cam comprisesa flat disc mounted in a housing and having ratchet teeth on itsperiphery. The disc is driven incrementally about a central shaft by apawl, which in turn is driven in a reciprocal manner by a synchronousmotor. At least one face of the disc is provided with arcuate camsurfaces which are concentrically arranged about the face or faces ofthe disc. Switch members are arranged to engage the arcuate cam membersupon rotation of the disc, and control various cycles of the appliance.

While the teachings of the present invention are set forth herein withparticular reference to a disc cam, it is to be understood that theinvention may also be employed as a drive mechanism for a drum cam. Ineither case, it is desirable that the disc or drum be driven at a veryslow rate of advance, since one rotation of the disc or drum shouldcomplete at least one entire cycle of the machine.

A wide variety of mechanisms have been proposed for advancing the camdisc or drum in a step-by-step manner. Generally, all of thesemechanisms include an array of ratchet teeth circularly arranged at theperiphery of the disc or at the end of the drum which are engaged by adrive pawl and a "no-back" pawl which prevents reverse rotation of theratchet teeth when the advancing pawl is retracted. The advancing pawlis incrementally driven by a cam or crank mechanism, and is retracted bya cam or spring mechanism while both pawls are entirely biased againstthe periphery of the ratchet by coil or cantilever wire springs. Anexample of a cantilever spring biasing the drive pawl into engagementwith the ratchet may be found in U.S. Pat. No. 3,738,185 and an exampleof coil springs biasing the drive pawl into engagement with the ratchetmay be found in U.S. Pat. No. 4,579,014. As may be appreciated fromthese patents, the assembly techniques involve precise hand operationsand careful handling of the timer until the timer is fully assembled.Moreover, such springs tend to become displaced if the timer is jarredduring installation or use.

SUMMARY OF THE INVENTION

The invention provides an incremental drive mechanism for a switchoperating timing cam. The drive mechanism includes a cam-driven slidewhich is mounted for reciprocation in a path which is tangential to aportion of the program cam having circularly arranged ratchet teeth. Theslide has a body portion and has a pawl arm portion which comprises acantilever spring arm having a pawl tooth at its distal end biased intoengagement with the ratchet teeth. The body portion of the slide hasfirst and second cam follower surfaces which are sequentially engaged bya radially extending cam portion of a camshaft which is rotationallydriven by a timer motor through a suitable set of reduction gears.

Engagement of the first cam surface by the radially extending cam causesthe slide to be driven rectilinearly, and causes said pawl to be drivenalong a rectilinear path in a first direction tangential to the ratchetteeth, to drive the teeth and the program cam through an arccorresponding to the arcuate width of an engaged tooth. The second camsurface of the slide, when engaged by the radially extending cam, causesthe slide to be driven rectilinearly and the pawl to be driven along apath in a second direction following the contour of at least one ratchettooth as the pawl is biased against the ratchet tooth by the cantileverspring arm. A retention or no-back pawl is provided to prevent theratchet teeth from moving in the second direction as the pawl followsthe contour of the engaged ratchet tooth.

An important aspect of the present invention is the fact that the slideis positively driven in its forward and reverse directions by a cam asopposed to an arrangement wherein movement is permitted by a cam whichresists spring-biasing exerted on the slide. Furthermore, the cam andits cam followers are arranged so that the cam is in engagement with acam follower during a major portion of an entire revolution of the cam,as opposed to prior art devices where the cam is out of driving contactwith a cam follower for up to 180 degrees of rotation.

While the normal operational bias of the ratchet teeth of the no-backpawl and the drive pawl is provided by the cantilever spring armsassociated with those pawls, it has been found that, under certainoperating conditions, the effectiveness of the biasing force provided bythe spring arms is dimenished. Under higher temperature environmentalconditions, cantilever spring arms fabricated from plastic materialstend to assume a permanent set if they become repeatedly "parked" at atooth crest during periods of nonoperation. The arms and their pawlstend to become permanently displaced from their original operatingpositions and, in some instances, the degree of displacement issufficient to inhibit the normal drive and/or no-back functions.

A further important aspect of this invention is to provide a mountingarrangement for the driven slide and the no-back base so that radialmovement of elements is permitted with respect to the circularlyarranged teeth on the timing cam. The extent of the movement is limitedto a degree not substantially exceeding the total spring movement of thecantilever arm. A spring biases the elements toward the teeth. Thisarrangement ensures that any permanent displacement of the cantileverspring arms will be compensated for by the biasing spring.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a timer according to this invention, withportions of the timer broken away to show details of the operation;

FIG. 2 is a fragmentary, exploded view of the cam drive mechanismaccording to this invention;

FIGS. 3 through 6 are plan views of the cam drive mechanism according tothis invention, showing the mechanism in successive positions during acycle of its operation;

FIG. 7 is a schematic representation of the path of travel of a pawlrelative to one set of ratchet teeth;

FIG. 8 is a schematic representation of the path of travel of a pawlrelative to another set of ratchet teeth;

FIG. 9 is a plan view of the no-back element and its biasing spring; and

FIG. 10 is a perspective view of the biasing spring.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, and particularly to FIG. 1, there isillustrated a sequential timer 10 for appliances such as dishwashers,clothes washers, clothes dryers, and the like, which includes a casing12. The casing 12 comprises two identical and mating halves 14 and 16,which cooperate to form a relatively narrow chamber 18. The matinghalves 14 and 16 are held together by a plurality of bolts or screws 20.A synchronous motor 22 (FIG. 2) is mounted on the casing half 16 byfasteners 24, and has an output shaft 26 which is keyed to and drives acamshaft 28 through a gear train (not shown) at a very slow rate ofspeed. The camshaft 28 has an advancing and retracting cam 30 whichextends from the camshaft 28 and is molded into the face of a supportingdisc 32.

The cam 30 cooperates with and drives a shuttle 34 in a rectilinearmanner along a path which is tangent to a cam disc 62. The shuttle 34has a body 35 which is provided with a pair of elongated apertures 36and 38 which respectively receive stationary pins 40 and 42, which aremolded into and project from the casing half 16. An additional aperture44 receives the camshaft 28. As may be seen in FIGS. 3 through 6, thecam 30 includes a cam surface 46 which curves from the arcutate surfaceof the camshaft 28 in such a manner that at least portions of thesurface 46 extend beyond any zone bounded by imaginary parallel lineswhich are tangent to the camshaft 28.

The shuttle 34 is reciprocated between the position illustrated in FIGS.3 and 5 by the engagement of the cam surface 46 with a cam surface 48 onthe shuttle 34. The cam surface 48 includes a straight surface 50 whichextends from a point of tangency between the cam surface 48 and thecamshaft 28, and by an arcuate surface 52 which extends from theaforementioned point of tangency. The curve of the surface 52 is definedby a radius corresponding to a line between the center of the camshaft28 and a tip 54 of the cam 30. Thus, as the cam surface 46 engages thesurface 50, as illustrated in FIG. 4, the shuttle 34 is driven to theright, as viewed in FIGS. 3 through 6. As the shuttle 34 is reciprocatedin this manner, a cantilever pawl arm 56 having a pawl tooth 58 isratcheted over one of a multiplicity of teeth 60 provided on the camdisc 62. As the tip 54 of the surface 46 traverses the arcuate camsurface 52, the pawl 58 tends to dwell in its retracted position at theend of its retraction stroke. During traversal of the tip 54 along thecam surface 52, the shuttle 34 is positively restrained from anyreciprocating movement, as may be seen in FIG. 5.

As the tip 54 leaves the cam surface 52, the cam surface 46 engages acam surface 64 on the shuttle 34 to drive the shuttle 34, and thereforethe pawl tooth 58, in a forward stroke to advance the cam disc 62 in acounterclockwise direction an angular distance corresponding to thecircumferential width of one of the teeth 60.

While the extent of the stroke of the pawl tooth 58 is determined by thespacing between the cam surfaces 50 and 64 and the distance between thetip 54 and the center of the camshaft 28, and while the stroke distanceis a fixed value, the degree to which the cam disc 62 is advanced isdependent upon the spacing between adjacent teeth 60. Thus, referringnow to FIGS. 7 and 8, it may be noted that the theoretical path oftravel of the pawl 58 is represented by the line 66, i.e., the path oftravel of the pawl tooth 58, ignoring interference by the teeth 60. InFIG. 7, the actual path of travel is from a point 68 to a point 70 andalong the periphery of one ratchet tooth 61 and along a portion of anadjacent tooth 63, as indicated by the arrows. The teeth 61 and 63illustrated in FIG. 7 are the smallest teeth in terms of arcuate extentthat the pawl tooth 58 may traverse, assuming a degree of travelindicated by the line 66, since any further travel would advance the camdisc 62 a total distance corresponding to the thickness of two teeth. Asis illustrated, however, the cam disc 62 would dwell as the pawl tooth58 advances from the point 70 to the illustrated position and would thenbe advanced as the pawl tooth 58 is advanced from its illustratedposition to the point 68. Thus, the total arcuate travel of the cam disc62 during one stroke of the pawl tooth 58 corresponds to the thicknessof a tooth measured at its base.

As may be seen in FIG. 8, the theoretical path of travel of the pawltooth 58 is identical to the path of travel 66 illustrated in FIG. 7.However, the thickness of a tooth 60a is almost twice the thickness ofthe tooth 60, illustrated in FIG. 7. The actual path of travel of thepawl tooth 58 is from its illustrated position to a point 72 along onlyone ratchet tooth 60a, so that there is substantially no lost motion ofthe pawl tooth 58 relative to the cam disc 62 upon the advancementstroke of the pawl tooth 58.

Thus, it may be appreciated that for single tooth advancement, thethickness of a tooth should be no greater than the distance traveled bythe shuttle 34, and no less than one-half that distance. Any tooth sizebetween these limits may be employed, and any such tooth size may berandomly placed along the periphery of the cam disc 60. These featuresenable the cam disc to be rapidly advanced through certain portions ofits rotative cycle by arranging relatively large teeth 60a along theperiphery of the cam segment and permits a relatively slow advance ofthe cam disc by arranging the teeth 60 along those segments of the discwhich are to be slowly advanced.

Retraction of the pawl tooth 58 along the sloped sides of a tooth 60 or60a tends to cause the cam disc 62 to rotate in a direction opposite itsdesired driven direction. Such rotation is arrested by a no-back pawlwhich comprises a base portion 80 (FIGS. 1, 2, and 9) mounted on thepins 40, 42, and the camshaft 28 which respectively extend throughapertures 84, 86, and a relieved portion 88 in the base 80. The base 80is further provided with a canatilever spring arm 90 having a pawl tooth92 at its distal end. The tooth 92 is biased into engagement with theteeth 60 or 60a, and prevents any retraction of the disc cam 62 counterto its desired driven direction.

Under certain elevated operating temperatures, the spring arms 56 and 90tend to assume a permanent set if they become repeatedly "parked" at thecrest of a tooth 60 during periods of nonoperation. Referring to FIG. 3,and with respect to the shuttle 34, the total possible movement of thearm 56 corresponds to an arc consisting of the arcuate measurement Splus the arcuate measurement T, where T corresponds to the height of theteeth 60 and S corresponds to the distance between a flattened portion100 of the pin 40 and a wall 102 of the elongated aperture 36.

A biasing spring 104 having spring fingers 106 and 108 is mountedbetween a bar 110 and a pair of posts 112 which project from the floorof the mating half 16. The spring finger 108 bears against the baseportion 80 of the no-back pawl, while the spring finger 106 bearsagainst the shuttle 34.

As initially constructed, the arm 56 biases a wall 113 of the elongatedaperture 36 against the pin 40 as the pawl 58 rides along the disc cam.If, however, the arm 56 assumes a permanent set inwardly toward the bodyportion 35, which is caused by adverse operating conditions, so that thearm 56 assumes an unbiased position located on the arc ST which is, asmeasured from the portion 35, greater than the arcuate distance T butwhich is, as measured from the disc cam 62, less than the arcuatedistance S, the spring finger 106 will tend to rotate the shuttle aboutthe pin 42 to maintain the pawl 58 in its illustrated position.

Similarly, and as illustrated in FIG. 9, the arm 90 biases a U-shapedwall portion 114 of the aperture 84 against the pin 40 as the pawl 92rides along the disc cam. If, however, the arm 90 assumes a permanentset inwardly toward the pin 40, which is caused by adverse operatingconditions, so that the arm 90 assumes an unbiased position located onthe arc ST which is, as measured from the body of the base portion 80,greater than the arcuate distance T but which is, as measured from thedisc cam 62, less than the arucate distance S, the spring finger 108will tend to rotate the base portion 80 about the pin 42 to maintain thepawl 92 in contact with all portions of the disc cam.

While the invention has been shown and described with respect to aparticular embodiment thereof, this is for the purpose of illustrationrather than limitation, and other variations and modifications of thespecific embodiment herein shown and described will be apparent to thoseskilled in the art, all within the intended spirit and scope of theinvention. Accordingly, the patent is not to be limited in scope andeffect to the specific embodiment herein shown and described, nor in anyother way that is inconsistant with the extent to which the progress inthe art has been advanced by the invention.

What is claimed is:
 1. In an incremental drive mechanism for a switchoperating timing cam comprising a housing means, a main program cam, anddrive means including a constant speed motor, said program cam having aset of circularly arranged one-way ratchet teeth having arcuate widthson its periphery, in combination therewith, the improvement comprisingdrive pawl means for driving said program cam in a step-by-step mannerby engagement of successive ratchet teeth, said drive pawl meansincluding camshaft means rotationally driven by said motor, saidcamshaft means having a periphery defining a radially extending cam, aslide rectilinearly driven by contact with said radially extending camin a direction substantially tangential to said circularly arrangedratchet teeth, guide means on said housing confining said slide torectilinear motion, said slide having a body portion and a cantileverpawl arm portion, said cantilever pawl arm portion comprising acantilever spring arm having a pawl tooth at its distal end biased intoengagement with said ratchet teeth, the body portion of said slidehaving a first cam follower surface and a second cam follower surface,said first cam follower surface and said second cam follower surfacebeing spaced apart and facing each other, said radially extending cambeing positioned between said first cam follower surface and said secondcam follower surface so that said first cam follower surface and saidsecond cam follower surface are sequentially engageable by said radiallyextending cam, said first cam follower surface, when engaged by saidcam, causing said slide to be driven rectilinearly and said pawl toothto be driven along a rectilinear path in a first direction tangential tosaid ratchet teeth to drive said teeth and the program cam through anarc corresponding to the arcuate width of an engaged tooth, said secondsurface, when engaged by said cam, causing said slide to be drivenrectilinearly and said pawl tooth to be driven along a path in a seconddirection following the contour of at least one ratchet tooth as saidpawl tooth is biased against said at least one ratchet tooth by saidcantilever spring arm, said guide means comprising a first pin extendingthrough a first slot in said slide and by a second pin extending througha second slot in said slide, said first slot being defined by first andsecond oppositely disposed walls, said cantilever pawl arm normallybiasing said first wall against said first pin, leaf spring meansbiasing said slide for rotation about said second pin so that, in theevent of any permanent deformation of said cantilever pawl arm towardsaid body portion, said leaf spring will bias said cantilever pawl armportion into contact with all portions of said disc cam, and means toprevent said ratchet teeth from moving in said second direction as saidpawl tooth is moving in said second direction.
 2. An improvement to anincremental drive mechanism according to claim 1, wherein said first andsecond cam follower surfaces are engaged by said radially extending camduring a major portion of a revolution of said camshaft.
 3. Animprovement to an incremental drive mechanism according to claim 2,wherein said radially extending cam extends beyond any zone bounded byimaginary parallel lines which are tangent to said camshaft.
 4. Animprovement to an incremental drive mechanism according to claim 3,wherein said first cam follower surface is a straight surface andwherein said second cam follower surface is comprised of a straightportion and a curved portion.
 5. An improvement to an incremental drivemechanism according to claim 4, wherein said curved portion has a radiusof curvature corresponding to the distance between the center of saidcamshaft and a tip of said radially extending cam.
 6. An improvement toan incremental drive mechanism according to claim 1, wherein saidarcuate width of an engaged tooth is less than the length of saidrectilinear path and greater than one-half the length of saidrectilinear path.
 7. An improvement to an incremental drive mechanismaccording to claim 1, wherein the path of said pawl tooth in said seconddirection is along one ratchet tooth and a portion of an adjacentratchet tooth.
 8. An improvement to an incremental drive mechanismaccording to claim 1, wherein the path of said pawl tooth in said seconddirection is along only one ratchet tooth.
 9. In an incremental drivemechanism for a switch operating timing cam, said mechanism being of thetype having a rectilinearly reciprocating slide and an associated pawlarm comprising a cantilever pawl arm carrying a pawl tooth at its distalend adapted to drive sequential circularly arranged teeth on said timingcam, the improvement comprising means for mounting said slide whichpermits said rectilinear movement in a direction tangential to saidcircularly arranged teeth and which permits movement of said slide insubstantially radial directions with respect to said circularly arrangedteeth, the extent of said movement in said substantially radialdirections being limited to a degree not substantially exceeding thetotal possible spring movement of said cantilever pawl arm, and biasingmeans for urging said slide toward said teeth.